Because metabolism was related to baseline smoking quantity, we examined whether the relations amongst metabolism, NRT condition, and relapse depended on smoking quantity. Heavier smoking at baseline was associated with higher likelihood of relapse (HR=1.34, 95% CI=1.17-1.53, p =2.5x10-5), but this relation did not differ by treatment status (interaction effect size=1.34, 95%CI=0.94-1.92, p=0.11). The interaction between CYP2A6-based metabolism and treatment remained significant (interaction effect size=2.55, 95%CI=1.19-5.46, p=0.016; Table S2), after adjusting for CPD. Similar results were found when FTND was used as a covariate.
